Convertible filters for treating vascular disease are known from the present inventor's own U.S. Pat. Nos. 6,267,776 and 6,517,559, the disclosures of which are hereby expressly incorporated herein by reference. These patents disclose numerous embodiments of convertible filters and particularly convertible filters suitable for treatment of vascular disease such as atherosclerotic and embolismic disease.
Generally, convertible filters include a filter structure having a plurality of filter legs arranged to form a single or double cone filter basket within the vessel lumen to trap blood borne clots or plaque with the vessel. A release member releasable secures the legs or filtering elements of the filter structure such that the filter may have two distinct configurations: filter or open/stent-like. The conversion is affected by release of the release member from the filter legs allowing the spring action of the filter legs themselves or of an externally applied opening force, such the force of a spring coupled to the filter legs, to open the filter legs from the filter configuration to the stent-like configuration. The release member may be a biodegradable material that deteriorates over time to release the filter legs to move to the stent-like configuration.
In another convertible filter, the release member is a mechanical retainer that includes a hook or similar grasping structure to allow the release member to be physically separated from the filter structure. Removal of the release member involves engaging the grasping structure with a snare and forcing the separation of the release member from the filter structure. The filter structure, which is typically attached to the wall by endothelial tissue, resists the applied force. The release member needs to be releasable from the filter legs with a minimum of force so that the reaction force exerted by the filter legs on the vessel wall does cause detrimental damage to the integrity of the wall. A well-designed release member will facilitate release of the member from the filter legs without transferring significant forces through the filter structure into the vessel wall.
Upon separation of the release member from the filter legs, the filter structure opens to assume the stent-like configuration along the wall of the blood vessel.